On microscopes, objectives having very different magnifications are often used sequentially and are quickly exchanged one with the other. The object fields corresponding to the objectives thereby vary very intensely in their magnitude and it is difficult to illuminate these different object fields uniformly well. It is practically impossible to illuminate object fields of objectives having a very high magnification of such as 100X as well as the object fields of scanning objectives with only a small magnification such as 1.25X with one individual condenser.
Two different condensors are often utilized for the above-mentioned extreme cases. U.S. Pat. No. 3,930,712 discloses a sub-stage illuminating device which includes two complete mutually exchangeable condensors disposed on a rotatable turret. In addition, a second rotatable turret is provided which enables contrasting elements to be pivoted into the illuminating beam path.
Such multi-condensors are very complex and expensive and require a great deal of space beneath the stage of the transmitted-light microscope equipped therewith.
Condensers are also known wherein the front lens for illuminating larger object fields can be removed, for example, by flipping them out or an auxiliary lens is additionally switched into the illuminating beam path beneath the aperture diaphragm. Such condensors are disclosed, for example, in British Pat. No. 1,423,691 and U.S. Pat. No. 4,521,076.
However, with one of these two measures alone, the entire region of object fields of different sizes for objectives having magnifications of 100X and 1.25X cannot be covered.
U.S. Pat. Nos. 3,799,645; 3,833,283; and, 4,136,927 disclose how the two above-mentioned measures can be combined with each other, namely the removal of the front lens and the switching in of the auxiliary lens. However, the auxiliary lens is here at a position far beneath the aperture-diaphragm plane so that the condenser must be of relatively long configuration and requires much space. In addition, when the auxiliary lens or also contrasting elements such as annular diaphragms for phase contrast are pivoted into the illuminating beam path, one must be certain that the aperture-iris diaphragm, which is stationary in the known condensors, is fully opened. If the danger of erroneous operations is to be avoided, additional constructive measures must be taken in order that the aperture diaphragm is opened automatically in specific switching positions. In this connection, reference may be made to the above-mentioned U.S. Pat. Nos. 4,521,076 as well as 4,368,947.